1. Field of the Invention
The present invention relates generally to variable pitch fans. More specifically, the present invention concerns a system for simultaneously adjusting the pitch of a plurality of fan blades attached to a common hub.
2. Discussion of Prior Art
Variable pitch fans are useful for a variety of applications such as, for example, commercial and industrial ventilation. Most ventilation fans are powered by electric motors. When fixed-blade ventilation fans are employed for commercial or industrial ventilation, the electric motor must typically either be switched on and off periodically or the speed of the electric motor must be adjusted as ventilation requirements vary due to environmental conditions. Periodically switching ventilation fans on and off is undesirable because it shortens the life of the electric motor. Further, periodically switching ventilation fans on and off does not continuously maintain the ventilated environment at a desired condition; rather, the ventilated environment is frequently in either an over-ventilated or under-ventilated state. Varying the speed of ventilation fans is undesirable because most electric motors have an optimum operating speed at which they are most efficient. Varying the speed of the electric motor above or below this optimal operating speed causes inefficiencies.
It is known that varying the pitch of propeller blades allows the drive motor to continuously operate at an optimum speed while adjusting for changes in output requirements. Although many systems exist today for varying the pitch of propeller blades such as, for example, variable pitch aircraft propellers, existing systems are typically too expensive, too complicated, and/or too bulky to be used for ventilation applications.
In accordance with an embodiment of the present invention, a pitch adjusting assembly is provided. The pitch adjusting assembly includes a first element presenting an elongated pin and a second element defining an elongated slot. The pin is movable about a first element axis and the slot is movable about a second element axis. The element axes are oriented substantially perpendicular to one another. The pin extends at least substantially parallel to one of the axes and the slot is elongated at least substantially parallel to the other of the axes. The slot receives the pin at a location offset from both axes.
In accordance with another embodiment of the present invention, a variable pitch fan blade assembly is provided. The variable pitch fan blade assembly includes a hub, a pitch adjusting assembly, a fan blade, and an actuator. The pitch-adjusting assembly is supported by the hub and includes a first element rotatable on a first axis and a second element rotatable on a second axis. The first element presents an elongated pitch pin. The second element defines an elongated pitch slot offset from the first and second axes. The pitch slot receives the pitch pin so that rotation of one of the elements causes rotation of the other of the elements. The fan blade is coupled to one of the elements. The actuator is coupled to the other of the elements.
In accordance with another embodiment of the present invention, a variable pitch fan blade assembly is provided. The fan blade assembly comprises a hub adapted for rotation on a hub axis and a fan blade pivotally coupled to the hub. The hub comprises a housing and a pitch wheel disposed within the housing. The housing is adapted to rotate on the hub axis and the pitch wheel is adapted to rotate relative to the housing on a pitch wheel axis. The fan blade is adapted to rotate with the housing around the hub axis. The fan blade is further adapted to rotate relative to the housing on a blade axis which is substantially perpendicular to the hub axis. The fan blade has a protruding pitch pin offset relative to the blade axis. The pitch pin is received in a slot in the pitch wheel. When the pitch wheel is rotated relative to the housing the fan blade is rotated on the blade axis, thereby adjusting the pitch of the fan blade.
In accordance with an embodiment of the present invention, a method of simultaneously varying the pitch of a plurality of fan blades using an actuator is provided. The method comprises (a) coupling a fan blade to a first element rotatable on a first axis; (b) coupling an actuator to a second element rotatable on a second axis; (c) inserting an elongated pin presented by one of the elements into an elongated slot presented by the other of the elements; (d) positioning the first and second elements so that the first and second axes are at least substantially perpendicular to one another; and (e) actuating the actuator to rotate the second element and thereby cause rotation of the blade.
The system of the present invention has the advantage of simultaneously adjusting the pitch of a plurality of fan blades. The system of the present invention has the further advantage of a relatively simple and inexpensive design. The system of the present invention has a still further advantage of being easily scalable for implementation in a wide variety of applications. The system of the present invention has an even further advantage of being substantially self-contained so that it can easily be used to replace existing fan blade assemblies without substantial modifications to the existing system. Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures.